Eight former longtime executives are suing Ralphs Grocery Co., alleging the company kept them aboard to help it merge with another grocery chain, then abruptly fired them. The lawsuit was filed earlier this month in Los Angeles County Superior Court. The former executives, all from Southern California, are seeking $15 million in compensatory damages for being laid off in May 1996, about 11 months after Compton-based Ralphs merged with Food 4 Less Supermarkets, according to the lawsuit filed Dec. 20. The executives, who each worked 18 or more years at the region's largest supermarket chain, accuse the company of fraud, deceit, age and sex discrimination and wrongful termination. Company executives would not comment on the lawsuit. Ralphs laid off more than 1,000 workers and closed more than 50 stores following the June 1995 $1.5-billion merger between the two companies. Ralphs was purchased by Yucaipa Cos., which then merged its Food 4 Less and Ralphs chains and named the combined company Ralphs Grocery Co. The lawsuit claims that the eight executives were assured for months, both publicly and privately by top company executives, that their jobs were secure in the wake of the merger.